Ferromagnetic amplifier and frequency converter



Feb. 19, 1963 R. w. DAMON 3,078,419

FERROMAGNETIC AMPLIFIER AND FREQUENCY CONVERTER Filed March 24, 1958 F/gl.

Signal Source Pump Energy Source In vemor: Ric/70rd W Damon,

by 72/ M H/'s Afforney.

3,078,419 FERROMAGNETEC AMPLEFIER AND FREQUENCY CONVERTER Richard W. Damon, Schenectady, N.Y., assigaor to General Electric Qompany, a corporation of New York Filed Mar. 24, 1958, her. No. 723,471 3 Claims. (Cl. 33t)4.6)

The present invention relates to an improved ferromagnetic system, and more particularly to an improved ferro-magnetic system for amplifying and for producing frequency conversion of microwave signals.

In a ferromagnetic amplifier the magnetic properties produced by unpaired spins of atomic electrons of ferromagnetic materials are utilized to produce amplification. Each electron spinning on its axis produces a magnetic field equivalent to that produced by a dipole magnet. And since electrons have mass, each spinning electron also has a gyroscopic action which, added to the magnetic effect, is approximately equivalent to a dipole magnet mounted on a gyroscope. When these ferromagnetic materials are immersed in a direct magnetic field, the dipole-magnet-gyroscopes process in unison about the field at a frequency, called the frequency of uniform precession, determined by the magnitude of the field.

When a microwave signal at a frequency equal to that of uniform precession is applied to a ferromagnetic ma terial at right angles to the direct magnetic field, the angle of precession increases With an increase in the magnitude of the microwave energy. For materials used in ferromagnetic amplifiers, this angle of precession increases with increasing microwave energy until this energy attains a certain magnitude called the threshold energy. Microwave energy above this threshold energy does not produce an increase in the angle of precession but rather couples into other modes of the ferromagnetic amplifier. These modes take two forms. They may be modes in the ferromagnetic material, called ma gnetostatic modes, which result from the dipole-magnetgyroscopes processing in different patterns rather than in unison the particular pattern depending upon the particular mode. That is, these dipole-magnet-gyroscopes precess in different phases and amplitudes at different points in the ferromagnetic material. Each magnetostatic mode is a different relationship between these phases and amplitudes. Or the modes may be modes of an electrical cavity resonator in which the ferromagnetic material is mounted. Of course these latter modes correspond to different configurations for the microwave magnetic and electric fields in the cavity resonator.

The lowest possible frequency for a magnetostatic mode equals 'y(HN M') wherein 'y is the gyromagnetic ratio for the ferromagnetic material, H is the applied direct field, N is a number between and 41r representing a demagnetization factor for the ferromagnetic material along a direction parallel to the applied field H, and M is the saturation magnetization of the ferromagnetic material. Of course, through control of the sizes and shapes of cavities, cavity modes can be found for frequencies over a wide range.

In ferromagnetic materials the energy above the threshold energy is usually coupled to pairs of modes the frequencies of which total to the frequency of the applied microwave energy, which is usually selected to be the same as the frequency of uniform precession. If the signal to be amplified has a frequency the same as one of these modes, energy is converted from the microwave energy to the frequency of this signal. In other words, energy is pumped from one frequency to the other. For this reason the frequency of the microwave energy is termed the pump frequency, and the source of this energy the pump source.

In the usual prior-type ferromagnetic amplifiers the pump energy and the signal energy are guided into a single wave guide cavity containing the ferromagnetic material. One disadvantage of this arrangement is that some means must be provided to eliminate the pump energy passing to the load side of the ferromagnetic material to prevent it from adversely affecting the load.

Accordingly, an object of the present invention is to provide a ferromagnetic amplifier wherein the pump wave energy is not in the same wave guide cavity with the signal wave energy.

Frequently, electrical cavity resonators are employed in ferromagnetic amplifiers to provide the modes needed for operation of the amplifier. But with energies of different frequencies in the same wave guide, as occurs in the prior ferromagnetic amplifiers, the tuning problem of the cavity resonators is rather acute because the same cavity must be tuned for at least two different frequencies. Such tuning is very difficult to obtain because a tuning movement towards one frequency is likely to be a detuniug movement for the other.

Thus, another object of the present invention is to provide a ferromagnetic amplifier having electrical cavity resonators, each one of which is tuned to only one frequency.

In conventional ferromagnetic amplifiers, signal energy reflected from the load is amplified by the ferromagnetic material and then guided to the source where often it has an undesirable effect.

Hence, another object is to provide a ferromagnetic amplifier in which signal energy reflected from the load is not amplified.

In the prior ferromagnetic amplifier, frequency conversion has been difficult due to the presence of several different frequencies in the same wave guide.

A further object of the present invention is to provide an improved ferromagnetic frequency conversion system.

These and other objects are achieved in one embodiment of my invention in which two wave guides are positioned to have a common wall through which a piece of ferromagnetic material extends. Signal energy is guided by one wave guide and the pump energy by the other. By suitable positioning of the ferromagnetic material in the wave guide, this material does not amplify energy reflected from the load.

The novel features believed characteristic of my inven-, tion are set forth in the appended claims. My invention itself, together with further objects andadvantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawing in which:

FIG. 1 is an embodiment of my invention in which there are no electrical cavity resonators,

FIG. 2 is a cross-sectional view of FIG. 1 taken along line 2-2 of FIG. 1,

FIG. 3 is an illustration of an embodiment of my invention in which two electrical cavity resonators are employed, 1

FIG. 4 is an embodiment of my invention in which one electrical cavity resonator is used, and

FIG. 5 is an embodiment of my invention in which a single cavity resonator is employed.

In the several figures of the drawing, corresponding elements have been indicated by corresponding reference numerals to facilitate comparison, and those circuit elements which may in themselves be entirely conventional and whose details form no part of the present invention have been indicated in simplified block form with appropriate legends. Referring now to FIG. 1, I have illustrated a first wave guide 11 for guiding signal energy of frequency f from a signal source 13 to a load 15. Another wave guide 17 guides pump energy of frequency f from a pump energy source 19. Wave guides 1i and 17 have a common wall 21 through which extends a piece of ferromagnetic material 23 that is preferably a single crystal. Any ferromagnetic material is suitable, but preferably it is a non-conductor such as manganese ferrite, nickel ferrite, and yttrium iron garnet, due to the skin-effect encountered with conductors. Although wave guides 11 and 17 are shown to be in parallel relationship with a common wall 21 extending along the total length of both wave guides, they need not be parallel and may have a common wall 21 for over only a short section of each. However, for compactness, it is best to have them parallel to one another. Also, the common wall may be a narrow one, rather than the wide one illustrated. The ferromagnetic material 23 is immersed in a direct magnetic field produced by poles 25 of an adjustable-strength magnet that is not shown in its entirety in order to simplify the illustration. The magnitude of the magnetic field from poles 25 is adjusted so that the frequency of uniform precession of the ferromagnetic material 23 is equal to the frequency f of the pumping source 19. This relationship is not absolutely necessary, but it is requisite for optimum operation. Material 23 must have a magnetostatic mode at the frequency of f of the signal source 13 or otherwise there will be no amplification of the signal source energy. Since the lowest possible frequency for a magnetostatic mode is 'y(HN M) the frequency of f of source 13 must be at least as great as the frequency of this mode. Material 23 also must have another magnetostatic mode at a frequency f wherein f =f -f The frequency f is called the idler frequency because it plays no direct part in the amplification process. That is, it is not directly related to the frequency of the pumping sources nor to the frequency of the signal source In FIG. 2 I have illustrated a cross-sectional view of the'embodiment of FIG. 1. Wave guide 11 is much larger than wave guide 17 because the frequency of the signal guided by wave guide 11 is much lower than the frequency of the signal guided by wave guide 17. The ferromagnetic material 23 is positioned at a distance x from a narrow wall of guide 11. As is disclosed in my application on Electromagnetic Coupling, Serial No. 494,921, filed March 17, 1955, and assigned to the as signee of the present invention, if

wherein a is the width of wave guide 11 along the wide side, and A is the free space wave length of the signal source energy of frequency h, the wave from source 13 has a'circularly polarized component of magnetic field at a distance x from one of the narrow walls. This component rotates in the same direction as the dipole gyromagnets in material 23 if this material is positioned from one of the narrow walls by distance x and rotates in the opposite direction if the material is positioned this distance from the other narrow wall. For amplification in the forward direction, the circularly polarized component from source 13 must be rotating in the same direction as the gyromagnets in the material 23. Then, the energy reflected from load 15 will have a circularly polarized component at the location of material 23 rotating in an opposite direction from the rotation of the dipole magnet gyroscopes and consequently will not amplify. Of course it is undesirable to have the reflected energy amplified because it may have a deleterious effect at source 13. Although for optimum directivity ferromagnetic material 23 should be located at position x for optimum amplification it should be positioned elsewhere because the position in the wave guide at which the maximum amount of amplification is obtained differs depending upon the particular magnetostatic modes used, Thus it may be de sirable to balance amplification against directivity and locate material 23 accordingly.

In FIG. 1, I have also illustrated a load 29 connected to the end of wave guide 17. If the system of FIG. 1 is to be used solely for amplification then load 29 may be omitted. But if frequency conversion is to be obtained, this load should be connected to the end of wave guide 17. The magnetostatic mode operating at frequency f produces a signal in wave guide 17 that can be conducted to load 2%. This signal has all the intelligence of the signal wave at frequency h, but a different fre quency. In other words the signal at frequency f can be considered to have been converted to a frequency f and applied to load 29. But simultaneously with this frequency conversion there is also amplification of the signal applied to load 15. Thus, it is possible to obtain signal amplification and frequency conversion simultaneously.

Although the system illustrated in FIG. 1 does function, a few modifications greatly improve the operation. First of all, if in wave guide 1'7 a cavity resonator is inserted that is tuned to the pumping frequency f the same amplification can be obtained with less pump energy. Also, at least one cavity resonator mode should be used for either the signal or idler frequency. Many pairs of magnetostatic modes have frequencies the sums of which equal the pump frequency f and which thus take energy from the desired modes f f It can be shown that if the applied direct magnetic field H is made greater than [(N +41r/2)]M, no two magnetic magnetostatic modes have frequencies totaling to f Thus, for proper operation in a semi-static mode the magnetic field should be made greater than this, and only one magnetostatic mode used in conjunction with one cavity resonator mode. Then the other magnetostatic modes cannot take energy from the system.

in FIG. 3 I have illustrated an embodiment of my invention containing the above-mentioned structure. I have not illustrated the sources of the signals, nor the loads, nor the magnet, in order to simplify the illustration. In wave guide 17 some irises 31 form a cavity resonator 33 tuned to frequency f and which includes ferromagnetic material 23. Material 23 is positioned an integral number of pump signal half wavelengths from one of these irises 31. Since cavity resonator 33 is tuned to frequency 1%,, much less pump energy is required for amplification purposes than is necessary in the embodiment of FIG. 1. In wave guide 11 I have placed a cavity resonator 35, formed by irises 37, which is tuned to the frequency h of the signal source 13. Material 23 is also positioned an integral number of half wavelengths at frequency h from one of these irises 37. In this ferromagnetic system only one magnetostatic mode is used and that is at a frequency f =f -f Of course, the magnetic field is adjusted for semi-static operation so that there are no two magnetostatic'modes the sum of the frequencies of which equal f If frequency conversion is also desired in the embodiment of FIG. 3, a signal at frequency f can be obtained at an end of wave guide 17 as was done in FIG. 1. Conceivably, cavity resonator 35 could be tuned to the frequency f and a magnetostatic mode at frequency 1, used. But this is not very practical since much of the signal source energy would be reflected from the cavity resonator 35 if it were tuned to a frequency other than f Also cavity resonator 35 could be tuned to frequencies 7; and f and no magnetostatic mode used. However, it is sometimes difificult to tune a cavity resonator to two given frequencies.

In FIG. 4 of the drawing I have illustrated an embodiment in which only the cavity resonator 33 is employed. If this cavity resonator is tuned to frequency i then less pump energy is required than otherwise. And if this cavity resonator is tuned to frequency f then only one magnetostatic mode at frequency f need be used.

In FIG. 5 I have illustrated an embodiment of my invention in which only the cavity resonator 35 is employed.

As previously mentioned, this cavity resonator should be tuned to frequency f and then only one magnetostatic mode at frequency f used. However, it is conceivable that cavity 35 resonator could be tuned to both frequencies f1 and f2- In summary, I have illustrated in certain embodiments a ferromagnetic system having two wave guides with a common wall, through which the ferromagnetic material extends, so that the signal source energy can be maintained in a separate wave guide from the pump energy. One advantage of this is that no elaborate means need be employed for eliminating the pump energy from the signal source wave guide. Also, with this arrangement the cavity resonators need not be tuned to more than one frequency, which simplifies the selection of cavity resonators. Further, through suitable positioning of the ferromagnetic material from the sides of the wave guides, energy reflected toward the source is not amplified and thus does not have a significant effect at the source of the signal. Still another advantage of this arrangement is that frequency conversion can be readily obtained.

While the invention has been described with respect to certain specific embodiments, it will be appreciated that many modifications and changes may be made by those skilled in the art Without departing from the spirit of the invention. I intend, therefore, by the appended claims, to cover all such modifications and changes as fall within the true spirit and scope of my invention.

What I claim is:

1. A system for amplifying a first signal by the extraction of energy from a second signal of higher frequency comprising a first waveguide means for coupling said first signal, a second separate waveguide means for coupling said second signal, a first electrical cavity resonator mounted to receive the signal from said first waveguide means and tuned to the frequency of said first signal, a second electrical cavity resonator mounted to receive the signal from said second Waveguide means and tuned to the frequency of said second signal wherein at least a portion of said second resonator adjoins said first resonator and has a wall adjacent at least a portion of said first resonator, a piece of ferromagnetic material of the type exhibiting precessional resonance mounted in said adjacent wall to extend partially into both said first and said second resonators and providing the communication therebetween, at least one of said resonators being otherwise entirely closed where the resonators adjoin, and means for immersing said ferromagnetic material in a direct magnetic field, the strength of which renders the frequency of uniform precession or" said material substantially equal to the frequency of said second signal, said ferromagnetic material in conjunction with said system providing a resonance at a frequency approximating the frequency difference between said first and second signals.

2. A system for amplifying a first signal by the extraction of energy from a second signal comprising a first waveguide having wide and narrow enclosing walls for propagating said first signal, a second waveguide having wide and narrow enclosing walls for propagating said second signal having a frequency greater than said first signal wherein at least a portion of said second waveguide has a wall common with at least a portion of said first waveguide, a piece of ferromagnetic material of the type exhibiting precessional resonance mounted in said first and second waveguides to provide communication therebetween, said waveguides being otherwise closed to one another, resonator means in said first waveguide for producing an enhanced magnetic field at said piece of ferromagnetic material at the frequency of said first signal, resonator means in said second waveguide for producing an enhanced magnetic field at said piece of ferromagnetic material at a frequency of said second signal, means for coupling said first signal into said first waveguide, means for coupling said second signal into said second waveguide, load means for extracting the amplified first signal from said first waveguide, and means for immersing said piece of ferromagnetic material in a direct field for establishing precessional resonance in said material at the frequency of said second signal, said direct field having a magnitude greater than (N |41r/2)M, wherein N, is a demagnetization factor for said ferromagnetic material parallel to said field and M is the saturation magnetization of said ferromagnetic material, said ferromagnetic material providing an additional resonance at a frequency approximating the frequency difference between said first and second signals.

3. The system as defined in claim 2 wherein said common wall is a wide wall for both said first and second waveguides and wherein said piece of ferromagnetic material is positioned at a distance from a narrow wall of said first waveguide approximately equal to wherein a is the width of a wide wall of said first waveguide and A is the free space wavelength of said first signal.

References Cited in the file of this patent UNITED STATES PATENTS 2,815,488 Von Neumann Dec. 3, 1957 2,825,765 Marie Mar. 4, 1958 2,848,688 Fraser Aug. 19, 1958 2,849,687 Miller Aug. 26, 1958 2,936,369 Lader May 10, 1960 2,978,649 Weiss Apr. 4, 1961 FOREIGN PATENTS 64,770 France June 29, 1955 (Addition to No. 1,079,880) 563,913 Belgium Jan. 31, 1958 OTHER REFERENCES Damon: Journal of Applied Physics, vol. 26, N0. 10, October 1955, pages 1281-1282.

Weiss: Physical Review, vol. 107, No. 1, July 1, 1957, page 317.

Dillon: Physical Review, vol. 105, Jan. 15, 1957, pages 759-760.

Suhl: Journal of Applied Physics, vol. 28, No. 11, November 1957, pages 1225-1235.

Landauer: Journal of Applied Physics, March 1960, pages 479-484.

Quantum Electronics, edited by Townes, Columbia University Press, New York, 1960, pages 306-313 (article by Fox), and pages 314-323 (article by Roberts et al.).

Damon et al.: IRE Transactions on Microwave Theory and Techniques, January 1960, pages 4-9. 

1. A SYSTEM FOR AMPLIFYING A FIRST SIGNAL BY THE EXTRACTION OF ENERGY FROM A SECOND SIGNAL OF HIGHER FREQUENCY COMPRISING A FIRST WAVEGUIDE MEANS FOR COUPLING SAID FIRST SIGNAL, A SECOND SEPARATE WAVEGUIDE MEANS FOR COUPLING SAID SECOND SIGNAL, A FIRST ELECTRICAL CAVITY RESONATOR MOUNTED TO RECEIVE THE SIGNAL FROM SAID FIRST WAVEGUIDE MEANS AND TUNED TO THE FREQUENCY OF SAID FIRST SIGNAL, A SECOND ELECTRICAL CAVITY RESONATOR MOUNTED TO RECEIVE THE SIGNAL FROM SAID SECOND WAVEGUIDE MEANS AND TUNED TO THE FREQUENCY OF SAID SECOND SIGNAL WHEREIN AT LEAST A PORTION OF SAID SECOND RESONATOR ADJOINS SAID FIRST RESONATOR AND HAS A WALL ADJACENT AT LEAST A PORTION OF SAID FIRST RESONATOR, A PIECE OF FERROMAGNETIC MATERIAL OF THE TYPE EXHIBITING PRECESSIONAL RESONANCE MOUNTED IN SAID ADJACENT WALL TO EXTEND PARTIALLY INTO BOTH SAID FIRST AND SAID SECOND RESONATORS AND PROVIDING THE COMMUNICATION THEREBETWEEN, AT LEAST ONE OF SAID RESONATORS BEING OTHERWISE ENTIRELY CLOSED WHERE THE RESONATORS ADJOIN, AND MEANS FOR IMMERSING SAID FERROMAGNETIC MATERIAL IN A DIRECT MAGNETIC FIELD, THE STRENGTH OF WHICH RENDERS THE FREQUENCY OF UNIFORM PRECESSION OF SAID MATERIAL SUBSTANTIALLY EQUAL TO THE FREQUENCY OF SAID SECOND SIGNAL, SAID FERROMAGNETIC MATERIAL IN CONJUNCTION WITH SAID SYSTEM PROVIDING A RESONANCE AT A FREQUENCY APPROXIMATING THE FREQUENCY DIFFERENCE BETWEEN SAID FIRST AND SECOND SIGNALS. 